The present invention herein resides in the art of digital imaging. More particularly, the present invention relates to digital imaging of a scene which has extreme lighting level differences. Specifically, the present invention relates to digital imaging of a video signal wherein the video signal is segmented according to respective gain level settings and wherein the segmented signals are recombined into a composite output signal presenting the most important information from the video signal.
In current video cameras and digital imaging capture systems, a gain setting or exposure level is set to enhance the presentation of the viewed image. These systems work well with scenes that are highly illuminated or where plenty of ambient light is present. For example, daytime or well lit rooms provide adequate lighting for viewing the scene with the video camera or sensing device. However, nighttime scenes are not easily viewed due to the lack of illumination. In order to enhance viewing of nighttime or poorly illuminated scenes, the gain setting or exposure time is increased to capture any ambient light available.
It is known that current systems are capable of adjusting the exposure or gain of the optical/electrical components within the sensor to provide viewable imaging as long as the scene""s ambient lighting remains within the sensitivity range of the sensor. Current sensors provide either overexposed or underexposed imagery if the ambient conditions exceed the dynamic range of a sensor at a given gain level. This results in the loss of useful scene information and over-illuminated or under-illuminated areas of the scene. In other words, a low gain video image only presents viewable information very near the predominate light source, whereas a high gain video image only presents useful image information away from the predominant light source.
It will be appreciated that poor lighting conditions are especially frustrating in military or aviation applications where a pilot is viewing a video monitor of an approaching target, at night, where the scenery includes bright city lights. Accordingly, the target locations within or near the city are not easily detected because of the lost video information. A wide range of lighting levels and their associated problems may also occur in night-time surveillance systems or police helicopter surveillance of urban areas.
In light of the foregoing, it is evident that there is a need to view a scene with a wide dynamic range and to present the scene in an image wherein the highly illuminated areas do not over-saturate the dimly illuminated areas so as to generate a composite image of the scene.
In light of the foregoing, it is a first aspect of the present invention to provide a dynamic range enhancement system.
Another aspect of the present invention is to provide a dynamic range enhancement system with a sensor to view an optical image, wherein the sensor has a video attenuator coupled thereto to adjust gain levels or exposure times to predetermined settings.
Yet another aspect of the present invention, as set forth above, is to provide a controller that is attached to both the sensor and the video attenuator to adjust the gain levels or exposure times at predetermined intervals.
Still another aspect of the present invention, as set forth above, is to time multiplex on a field basis between unattenuated (high gain) and attenuated (low gain) video signals such that both high and low gain video signals are available simultaneously for analysis.
A further aspect of the present invention, as set forth above, is to provide a combiner which receives the high gain and low gain video signals and combines them into a composite signal with minimal saturation.
Yet a further aspect of the present invention, as set forth above, is to provide a normalizer which receives the composite video signal to reduce the dynamic range of the signal while preserving important scene information content for viewing by the human eye.
The foregoing and other aspects of the present invention which shall become apparent as the detailed description proceeds are achieved by a system for enhancing the dynamic range of an imaging signal, comprising a sensor for viewing a scene having a wide dynamic range and generating a digital image signal of the scene; an attenuator coupled to the sensor for selectively attenuating the digital image signal; a demultiplexer for receiving the digital image signal and grouping like attenuated signals into at least a first gain signal and a second gain signal; and a combiner for receiving the first and second gain signals and producing a combined image signal with minimum saturation.
Other aspects of the present invention are attained by a method for enhancing an imaging signal, comprising the steps of viewing a scene with a sensor that generates a digital image signal representative of the scene; coupling an attenuator to the sensor to generate different exposure levels while generating the digital image signal; demultiplexing the digital image signal into at least a first digital image signal and a second digital image signal corresponding to attenuation levels set by the attenuator; combining the first and second digital image signals to produce a composite image signal containing both low and high illuminated areas of the scene with minimal saturation.